The invention has as its object a new process for obtaining chemical compounds that are derived from polyunsaturated fatty substances, whereby said compounds are characterized by the presence, along the linear hydrocarbon-containing chain, of one or more branches of at least two carbon atoms.
These compounds are obtained by adding olefins to polyunsaturated fatty substances in the presence of a nickel catalytic system.
These unsaturated codimers can be hydrogenated, and saturated fatty substances that are characterized by a melting point that is generally below xe2x88x9220xc2x0 C., significant thermostability, and desired surfactant properties are then obtained.
The presence of branches in the compounds with a fatty substance base, mainly when these branches are located toward the center of the linear chains that comprise 14 to 18 carbon atoms, is reflected by a certain number of remarkable properties, such as, for example:
the very significant lowering of melting points, pour points and cloud points and an appreciable increase of the viscosity of the branched fatty substances relative to the same unbranched linear compounds; this property is used, for example, in lubricants, fats or plasticizers, where esters of fatty substances, salts or branched alcohol esters, whose acid can be organic or mineral, are used;
the reduction of the surface tension and the interfacial tension, whereby these characteristics are still studied in the field of surfactants and emulsifiers; this reduction makes it possible to obtain lower CMC (Critical Micellar Concentration);
the inhibition of the crystallization of branched soaps that may or may not be mixed with standard soaps, which makes it possible to obtain transparent soaps;
an increase of hydrophilicity, which makes the branched compounds more soluble or more wettable; a possible use would be to use quaternary salts of branched fatty acids in the emollients where softening is on an equal footing with a certain wettability;
a modification of the surface of the molecule, surface characterized by gaps that are created by the presence of branches; the cosmetic application of this property makes it possible to consider skin cream formulas which allow water vapor to pass, for example bases that consist of branched acid esters or even esters where the acid and the alcohol are both branched;
increased solubility of heavy metal salts with branched acids, which makes them soluble either in water or in certain organic solvents; the applications are multiple such as drying agents in paints, such as pigments, in the extraction of metals or anticorrosion, where it is possible to use calcium salts, alcanolamine salts or even amine salts as active agents. The branched acid salts also offer a greater compatibility of certain mineral feedstocks with polymers, which makes it possible to increase the feedstock ratio in plastics;
the bactericidal or bacteriostat effect that is more or less pronounced according to the nature of the bacteria and the number or magnitude of branches makes it possible to protect creams against bacterial attack or to replace quaternary salts in formulations that may or may not be basic; another use exists as an inhibitor of the evaporation of water, where, for example, compounds such as a branched alcohol or a branched acid monoglyceride make it possible to delay biodegradability and therefore to save the inhibitor.
The reaction of olefins with butadiene or other dienes has been known for a long time and was the object of several reviews. The codimerization of butadiene with ethylene leads to hexadiene-1,4; codimerization of ethylene with isoprene leads to methyl-3 hexadiene; and, finally, by codimerization of ethylene with piperylene, vinyl-2-pentane is obtained. Many catalysts are used to carry out these reactions. It is possible to cite, for example, rhodium, ruthenium, palladium, cobalt, iron, or nickel systems. Systems with a titanium base have been described (Connel, Laurence G.-Ann. N.Y. Acad. Sci. (73), 214, 143-9) to catalyze the formation of vinylcyclobutane from ethylene and butadiene.
In contrast, the addition of olefin to functional dienes has rarely been described. U.S. Pat. No. 3,742,080 points out the possibility of adding ethylene to dienes, of which one or two ends of the hydrocarbon-containing chains are substituted by halogen or alkoxy groups.
It is also known that an olefin can react on a conjugated diene or triene compound according to a Diels-Alder-type reaction. For example, the addition of ethylene to polyunsaturated fatty substances by simple heating to a temperature of 290xc2x0 C. is described (R. E. Beal et Coll. JAOCS 52, 400 (1975)). Thus, a compound that has an unsaturated cycle with 6 carbon atoms in its hydrocarbon-containing chain is obtained from methyl linoleate and ethylene. After hydrogenation, these compounds have advantageous properties. Their melting point, however, which is above 10xc2x0 C., is still too high to allow them to be used as lubricants.
Another method for obtaining branched compounds of fatty substances is known. It consists in reacting, according to a Wittig-type reaction, a ketone, such as, for example, the methyl ester of 12-oxo octadecanoic acid with an ylide, for example, the link P(Ø)3xe2x95x90CHCH3, where Ø represents a phenyl radical. The compound CH3(CH2)5C(xe2x95x90CHCH3)(CH2)10COOCH3, which can be hydrogenated into methyl ethyl-12-octadecanoate, is then obtained (D. G. Chasin et Coll, Chem. Phys., Lipids (71) 6, 8-30).
In nature, the presence of branched saturated compounds of fatty substances that are found in Koch bacteria, for example, or, with another length of hydrocarbon-containing chain, in mutton fat has also been pointed out.
Finally, it is known that the products that are referred to as xe2x80x9cisostearicxe2x80x9d contain traces of compounds that carry ethyl- or vinyl-type branches.
Recently, international patent applications WO-A-91/11428, 91-11427, 91/11426, and 91/11425 described obtaining branched fatty substance compounds by a catalytic process. The addition of olefin, such as ethylene or propylene, to the polyunsaturated fatty substance, a linoleic acid ester, for example, is catalyzed by a system with a base of rhodium, iridium, palladium, or ruthenium. The systems with rhodium, which are the only ones to have been described in an obvious way, are not very active, however.
U.S. Pat. Nos. 5,476,956 and 5,434,282 describe the use of a very specific rhodium catalytic system that makes it possible to accelerate the addition of olefin to the fatty substance dienes, particularly conjugated dienes, by a factor of 50 to 100. This process, however, is still very difficult to apply on a large scale due to excessive rhodium consumption.
Published French Patent Application FR-A-2 766 482, in the name of the same applicant, describes a process that uses a cobalt catalytic system, which consists in reacting simple olefins, for example ethylene, on polyunsaturated esters, for example the methyl linoleate that may or may not be conjugated, to obtain branched esters. The branched compounds that are obtained can be hydrogenated and used, among other things, as lubricant bases. This patent application describes a process for obtaining a codimer in which co-catalysts can optionally be introduced, such as, for example, transition metals such as iron, nickel, copper, rhodium or palladium. These catalysts make it possible to catalyze the conjugation, if a start is made from an unconjugated polyenic ester, and therefore to accelerate the reaction.
It has now been found, surprisingly enough, that by using a simple nickel compound with an acid reducing agent or a reduced nickel compound with a Bronsted or Lewis acid, it was possible, in the presence of a ligand, to obtain the main reaction of ethylene addition or another olefin to the ester, which may or may not be conjugated, under particularly mild conditions, since it is possible to obtain total conversion of conjugated esters with less than 0.1 MPa of ethylene pressure and between 30 and 80xc2x0 C. In addition, thanks to the increased reactivity of these nickel catalysts, it is possible to obtain the addition of 2 or 3 ethylene radicals on the diene substrate.
Whereby nickel is highly conjugating, it is possible in one stage also to obtain an addition product by starting from a polyenic ester that is not conjugated but can be conjugated.